And in Louisiana, 24 candidates are running in an all-party “jungle” primary, with the top two vote-getters advancing to a December 10 runoff, which could potentially decide the balance of power in the Senate.

If Kennedy and Boustany can both clear the runoff, the GOP would be guaranteed of keeping the seat, now held by U.S. Senator David Vitter. But if Campbell or Fayard can come through, the December 10 runoff will be the last word on Senate races this year — and, if the Senate is closely divided, decide which party controls the chamber.

In addition to Rubio and Burr, Republican incumbents are seeking re-election in Alabama, Arkansas, Georgia, Kentucky, Oklahoma and South Carolina.